1. Field of the Invention
The present invention relates to a filter for spray ducts of dental or surgical handpieces.
2. Description of the Related Art
Dental or surgical handpieces have extremely thin ducts through which the spray water and/or spray air is conducted to the tip of the instrument where the medium is applied usually in the form of a spray to the work area for cooling and for removing removed tooth or bone material.
Because of the extremely small diameters of the spray ducts in the instrument, the ducts sometimes become clogged.
The most obvious solution of this problem, which is to provide an appropriate fine filter in the supply unit, is not used for various reasons. One reason is the fact that a not insignificant portion of the impurities emanate from the O-ring seals between the supply hose and the handpiece. These O-rings are subjected to shearing loads when they are mounted or when the handpieces are removed, which together with the geometry of the coupling leads to the abrasion of small rubber particles.
It must additionally be pointed out that the manufacturers of the supply units, in which also various control and regulating devices for the dental or surgical handpieces are provided, usually are not the manufacturers of the handpieces; rather, the supply units are manufactured by separate manufacturers who specialize in producing hospital and medical supplies.
However, since the users of the handpieces are to be protected as much as possible from these problems and since the repairs in the case of clogging of the lines must be carried out by the maintenance service of the manufacturers of the handpieces, there is an increasing demand for providing filters which protect the handpiece.
For example, EP 0 591 953 A provides a solution in which cylindrical filter cartridges are mounted in the area between the supply hose and the headpiece head; however, this requires a large amount of space and additionally makes it necessary to periodically replace the cartridges. Even though this activity is to be preferred over a repair, it is still an unpleasant fine-mechanical activity which has to be carried out by the physician or his or her assistant; this means that the replacement will be delayed as long as possible and the device is still operated when the filter is actually already unduly clogged and leads to a pressure drop.
Another solution is disclosed in U.S. Pat. No. 5,716,210. A filter piece is inserted between the handpiece and the supply hose, wherein the filter piece is provided with corresponding connections for the supply hose and the handpiece. This solution has the advantage that the filter piece can be easily replaced; the disadvantages are the high costs of such an intermediate filter piece and the mechanical problems which always occur when all releasable connections are doubled, and of course the fact that the filter piece is located upstream of the O-ring seals of the handpiece.
In addition, the filters themselves are so small that in many cases a large portion of their pores are clogged already after filtering out a few particles and are no longer capable of operating. This is primarily due to the fact that the filter surface must be located within the cross-section of the spray duct and, therefore, leads already in the empty state to a considerable reduction of the available cross-section.